Deprotection of oximes, phenylhydrazones, semicarbazones and thiosemicarbazones to the corresponding carbonyl compounds using cetyltrimethylammonium peroxodisulfate as a new and selective oxidizing agent

Article abstract of DOI:10.1002/jccs.200800074

Cetyltrimethylammonium peroxodisulfate (CTA)₂S₂O ₈ was quantitatively prepared and used for the deprotection of oximes, phenylhydrazones, semicarbazones and thiosemicarbazones to the corresponding carbonyl compounds in acetonitrile. Its agent is more efficient and has advantages over similar reagents in terms of the amount of oxidant, short reaction time, simple work up, and high yield.

Full text of DOI:10.1002/jccs.200800074

508
Journal of the Chinese Chemical Society, 2008, 55, 508-511
Communication
Deprotection of Oximes, Phenylhydrazones, Semicarbazones and
Thiosemicarbazones to the Corresponding Carbonyl Compounds Using
Cetyltrimethylammonium Peroxodisulfate as a New and Selective
Oxidizing Agent
Mohammad Norouzi,a Mahmood Tajbakhsh,b* Heshmatollah Alinezhadb and Azade Geran Urimib
aDepartment of Chemistry, Payame Noor University, Sari, Iran
bDepartment of Chemistry, Mazandaran University, Babolsar 47416-1467, Iran
Cetyltrimethylammonium peroxodisulfate (CTA)2S2O8 was quantitatively prepared and used for the
deprotection of oximes, phenylhydrazones, semicarbazones and thiosemicarbazones to the corresponding
carbonyl compounds in acetonitrile. Its agent is more efficient and has advantages over similar reagents in
terms of the amount of oxidant, short reaction time, simple work up, and high yield.
Keywords: Cetyltrimethylammonium peroxodisulfate; Deprotection; Oxime; Phenylhydrazone;
Semicarbazone; Thiosemicarbazone.
INTRODUCTION
(CTA)2S2O8 was characterized by its spectroscopical and
physical data.
Derivatives of carbonyl compounds such as oximes,
phenylhydrazones, semicarbazones and thiosemicarba-
zones are used not only for the characterization and purifi-
cation of carbonyl compounds but also play an important
role in the protection of carbonyl compounds, as they are
highly crystalline and stable compounds. Thus, the regen-
eration of carbonyl compounds from their derivatives un-
der mild condition is important process in organic synthetic
chemistry.
RESULTS AND DISCUSSION
To find the optimum reaction conditions, we have
chosen the C=N derivatives of the benzaldehyde as a model
substrate. When we have treated the C=N compounds with
reagent in different solvents, temperatures and mole ratio
of substrate to reagent, we have found that a 1:1 mole ratio
of substrate to reagent in refluxing acetonitrile gives the
highest yeild of the corresponding carbonyl compound
(Table 1, ertry 1).
The classical method for the cleavage of oximes,
phenylhydrazones, semicarbazones and thiosemicarba-
zones to aldehydes and ketones is acid hydrolysis which is
not suitable for acid sensitive compounds.1 Several depro-
tection methods have been developed which have some ad-
vantages over the classical hydrolysis method.2-15
We report here a new and efficient procedure for the
cleavage of oximes, phenylhydrazones, semicarbazones
and thiosemicarbazones using cetyltrimethylammonium
peroxodisulfate. The results obtained with this reagent are
satisfactory and proved that it is a valuable addition to the
existing oxidants.
In order to show the applicability and generality of
this method we have examined the reaction of benzylic, al-
lylic and aliphatic oximes, phenylhydrazones, semicarba-
zones and thiosemicarbazones with (CTA)2S2O8 in reflux-
ing acetonitrile (Scheme I).
The results are tabulated in Table 2. As indicated in
this Table, varieties of C=N derivatives are converted to the
parent C=O compounds in excellent yeild under optimum
reactions condition (Table 2, entries 1-34). It is noteworthy
that, unlike other oxidative hydrolytic methods, the major
drawback of overoxidation of the resulting aldehydes, is
not observed under the reaction conditions. Interestingly
the a,b-unsaturated derivatives underwent deprotection
(CTA)2S2O8 is easily prepared by addition of an aque-
ous solution of cetyltrimethylammonium bromide to a so-
lution of potassium peroxodisulfate in water.16 The isolated
* Corresponding author. E-mail: tajbaksh@umz.ac.ir

Cetyltrimethylammonium Peroxodisulfate
J. Chin. Chem. Soc., Vol. 55, No. 3, 2008 509
Table 1. Deprotection of C=N derivatives of benzaldehyde under different conditions using
CTAP
Mole ratio
Reaction period
Yield (%)a
(min)
Entry
Solvent
Temperature
(Substrate/Reagent)
1
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
C3H6O
C3H6O
C3H6O
C3H6O
C3H6O
C3H6O
THF
Reflux
Reflux
Reflux
r.t
1:1
2
2
92-98
92-98
75-80
20-30
20-30
05-10
75-90
75-90
30-50
10-15
10-15
0-5
2
1:2
3
1:0.5
1:1
2
4
60
60
60
10
10
10
60
60
60
60
60
60
60
60
60
60
60
5
r.t
1:2
6
r.t
1:0.5
1:1
7
Reflux
Reflux
Reflux
r.t
8
1:2
9
1:0.5
1:1
10
11
12
13
14
15
16
17
18
19
20
r.t
1:2
r.t
1:0.5
1:1
Reflux
r.t
60-75
0
THF
1:1
CH2Cl2
CH2Cl2
CHCl3
CHCl3
n-C6H6
n-C6H6
Reflux
r.t
1:1
35-50
0
1:1
Reflux
r.t
1:1
20-30
0
1:1
Reflux
r.t
1:1
05-10
0
1:1
a Yields refer to isolated products.
for the regeneration of carbonyl compounds from oximes,
phenylhydrazones, semicarbazones and thiosemicarba-
zones that possess significant advantages over the existing
methods such as simple procedure, high yield and mild re-
action conditions.
Scheme I
NX
O
(CTA)2S2O8
CH3CN/Reflux
R1
R1
R2
R2
X = OH, NHC6H5, NHCONH2, NHCSNH2
R1 = Alkyl, Aryl, Vinyl
EXPERIMENTAL SECTION
R2 = Alkyl, Aryl, H
Products were isolated and their physical data were
compared with those of known samples. Solvents were
freshly distilled. Oximes, phenylhydrazones, semicarba-
zones and thiosemicarbazones were prepared according to
the described procedure.17
(CTA)2S2O8 = Cetyltrimethylammonium peroxodisulfate
very efficiently without affecting the olefinic bond and the
reaction is essentially chemoselective (Table 2, entries 13,
22, 28, 34). Furthermore, functional groups such as chloro,
bromo, methoxy, hydroxy, nitro, and alkyl were also inert
to this reagent and no byproduct formation was observed
(Table 2, entries 3-9, 15-19, 24-26, 30-32).
Preparation of Cetyltrimethylammonium Peroxo-
disulfate, [(CH3(CH2)14N(CH3)3)]2S2O8, (CTA)2S2O8
To a solution of hexadecyl trimethylammonium bro-
mide (3.7 g, 10 mmol) in 75 mL of water K2S2O8 (1.3 g, 5
mmol) in 100 mL of water was added dropwise and the re-
action mixture was stirred for 20 min at room temperature.
A white solid was formed. The precipitate was filtered,
washed with cold distilled water (50 mL) and dried under
vacuum over calcium chloride to afford a white powder.
The yield of (CTA)2S2O8 was 92%; it decomposes at 125
°C to a light brown material.
To show the advantage and drawbacks of this method
we have compared some of our results with those reported
in the literature. As indicated in the Table 3, (CTA)2S2O8
compared to the other reagents, performs this transforma-
tion in higher yield, shorter reaction times, and milder reac-
tion conditions.
In conclusion, we have developed an efficient method

510 J. Chin. Chem. Soc., Vol. 55, No. 3, 2008
Norouzi et al.
Table 2. Deprotection of oximes, phenylhydrazones, semicarbazonees and thiosemicarba-
zones with (CTA)2S2O8 in acetonitrile at reflux
Entry
Substrate
t/min
Productsa
Yield (%)b
1
2
C6H5CHNNHC6H5
(C6H5)2CNNHC6H5
02
22
24
15
25
20
08
08
25
60
60
30
25
20
22
24
35
12
22
35
60
40
15
19
22
28
60
40
15
18
20
25
60
40
C6H5CHO
(C6H5)2CO
96
90
87
95
94
93
96
93
95
75
60
92
88
93
92
92
69
90
94
90
45
80
96
93
94
90
70
80
97
96
91
87
73
80
3
4
o-ClC6H4CHNNHC6H5
p-ClC6H4CHNNHC6H5
o-MeC6H4CHNNHC6H5
m-MeOC6H4CHNNHC6H5
p-HOC6H4CHNNHC6H5
5-Br, 2-HOC6H3CHNNHC6H5
C6H5C(p-CIC6H4)NNHC6H5
C6H5CH2CHNNHC6H5
(CH3(CH2)5)(CH3)CNNHC6H5
(C6H5CHCH)2CNNHC6H5
C6H5(CH)2CHNNHC6H5
C6H5CHNOH
o-ClC6H4CHO
p-ClC6H4CHO
o-MeC6H4CHO
m-MeOC6H4CHO
p-HOC6H4CHO
5-Br, 2-HOC6H3CHO
C6H5(p-CIC6H4)CO
C6H5CH2CHO
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
(CH3(CH2)5)(CH3)CO
(C6H5CHCH)2CO
C6H5(CH)2CHO
C6H5CHO
p-MeOC6H4CHNOH
p-ClC6H4CHNOH
p-NO2C6H4CHNOH
C6H5C(p-CIC6H4)NOH
p-ClC6H4C(CH2CH3)NOH
(C6H5)2CNOH
p-MeOC6H4CHO
p-ClC6H4CHO
p-NO2C6H4CHO
C6H5(p-CIC6H4)CO
p-ClC6H4COCH2CH3
(C6H5)2CO
C6H5CH2CHNOH
C6H5(CH)2CHNOH
C6H5CHNNHCONH2
p-MeOC6H4CHNNHCONH2
p-ClC6H4CHNNHCONH2
p-ClC6H4C(CH2CH3)NNHCONH2
C6H5CH2CHNNHCONH2
C6H5(CH)2CH NNHCONH2
C6H5CHNNHCSNH2
p-MeOC6H4CHNNHCSNH2
p-ClC6H4CHNNHCSNH2
p-ClC6H4C(CH3)NNHCSNH2
C6H5CH2CHNNHCSNH2
C6H5(CH)2CHNNHCSNH2
C6H5CH2CHO
C6H5(CH)2CHO
C6H5CHO
p-MeOC6H4CHO
p-ClC6H4CHO
p-ClC6H4CO CH2CH3
C6H5CH2CHO
C6H5(CH)2CHO
C6H5CHO
p-MeOC6H4CHO
p-ClC6H4CHO
p-ClC6H4COCH3
C6H5CH2CHO
C6H5(CH)2CHO
a All the products were characterized by comparison of their IR and 1H NMR spectra with
authentic samples.17 b Yields refer to isolated products.
Table 3. Deprotection of oximes, phenylhydrazones, semicarbazones and thiosemicarbazones by (CTA)2S2O8 in
comparison with other reagents
Reagent:Sustrate
(mol ratio)
Time
(min)
Substrate
Reagent
Temp/Solvent
Reflux/CH3CN
Yield Ref.
C6H5CHNNHC6H5
C6H5CHNOH
2
20
15
15
16
20
15
120
20
240
60
96
93
96
97
96
93
97
95
100
72
85
(CTA)2S2O8
1:1
C6H5CHNNHCONH2
C6H5CHNNHCSNH2
C6H5CHNNHC6H5
C6H5CHNOH
2,6-DCPFCa
1:1
3:1
r.t/CH3CN
18
C6H5CHNNHCONH2
C6H5CHNNHC6H5
C6H5CHNNHCONH2
C6H5CHNNHCONH2
C6H5CHNOH
Caro’s Acid/Silica Gel
Reflux/CH2Cl2
15(e)
ACCb/Alumina
3-CPCCc
1:1
2:1
Reflux/CH2Cl2
Reflux/CH2Cl2
19
3(b)
a 2,6-dicarboxypyridinium fluorochromate. b Ammonium chlorochromate. c 3-Carboxypyridinium chlorochromate.

Cetyltrimethylammonium Peroxodisulfate
J. Chin. Chem. Soc., Vol. 55, No. 3, 2008 511
155.
General Procedure for Deprotection of Oximes,
Phenylhydrazones, Semicarbazones and Thiosemicar-
bazones with (CTA)2S2O8
7. Gurini, M.; Epifano, F. Synth. Commun. 1999, 29, 541.
8. Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A.; Zarei, A. J.
Chin. Chem. Soc. 2004, 51, 509.
In a round-bottomed flask (50 mL) equipped with a
magnetic stirrer, a mixture of the substrate (1 mmol) in
CH3CN (5 mL) and (CTA)2S2O8 (1 mmol) was placed. The
and stirred at reflux temperature for the specified time (Ta-
ble 2). The progress of the reaction was monitored by TLC.
After the reaction was completed the mixture was filtered,
and the solid material was washed with diethyl ether (2 ´ 10
mL). The combined filtrate was evaporated under reduced
pressure to afford pure carbonyl compound in 45-97%. If
necessary, the products were further purified on a silica-gel
plate or silica-gel column with appropriate eluent.
9. Zhang, G. S.; Yang, D. H.; Chen, M. Synth. Commun. 1998,
28, 721.
10. Ho, T. L.; Jana, G. H. J. Chin. Chem. Soc. 1999, 46, 639.
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12. Bandgar, B. P.; Makone, S. S. J. Chin. Chem. Soc. 2000, 47,
575.
13. Kuo, Y. H.; Jang, T. L. J. Chin. Chem. Soc. 1991, 38, 203.
14. Gui-Sheng, Z.; Bing, C. Synth. Commun. 2000, 30, 2507.
15. (a) Tajbakhsh, M.; Mohammadpoor-Baltork, I.; Ramzanian-
Lehmali, F. Phosphorus, Sulfur Silicon Relat. Elem. 2003,
178, 2621. (b) Tajbakhsh, M.; Mohammadpoor-Baltork, I.;
Ramzanian-Lehmali, F. J. Chem. Res. (s). 2003, 710. (c)
Tajbakhsh, M.; Hosseinzadeh, R.; Sadatshahabi, M. Synth.
Commun. 2005, 35, 1547. (d) Hosseinzadeh, R.; Tajbakhsh,
M.; Ramzanian-Lehmali, F.; Sadatshahabi, M. Phosphorus,
Sulfur Silicon Relat. Elem. 2005, 180, 2279. (e) Tajbakhsh,
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1985, 13, 221. (b) Gratzel, C. K.; Jirousek, M.; Gratzel, M.
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ACKNOWLEDGEMENTS
Financial support from research council of Mazandaran
University is gratefully acknowledged.
Received August 6, 2007.
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